#include <stdio.h>
#include <string.h>

void main()
{
    char clearText[100],cipherText[100];
    int i,j,k,t;
	int key=3; 

    printf("please input clearText\n");
    gets(clearText);
        
    for(i=0; i<strlen(clearText); i++)
    {
        if(clearText[i] >= 'A' && clearText[i] <= 'Z')
        {
            cipherText[i] = ((clearText[i]-'A')+key)%26+'A';
        }
        else if(clearText[i] >= 'a' && clearText[i] <= 'z')
        {
            cipherText[i] = ((clearText[i]-'a')+key)%26+'a';
        }
    }
    printf("%s", cipherText);
}
